Granulysin is a 9 kD alpha-helical protein expressed by human natural killer cells and T lymphocytes. Recombinant granulysin lyses both mammalian cells and a broad spectrum of microbes. Synthetic peptides (10-30 residues) corresponding to the central region of granulysin recapitulate its lytic activity. In a subset of these peptides, replacement of cysteine or arginine residues, or introduction of D-amino acids to disrupt the alpha-helix, results in the loss of activity against mammalian cells with little or no decrease in antimicrobial activity. The goal of this Project is to synthesize immunotherapeutics based on the granulysin sequence for biodefense and for treatment of antibiotic resistant organisms. The specific aims are: 1) prepare additional substituted peptides that exhibit increased potency and microbial specificity; 2) use a subset of the peptides identified in Aim 1 to develop compounds with higher activity and stability by preparing linear arrays, dendrimers, cyclized peptides, and peptides containing unnatural amino acids; and 3) use biophysical methods, including analytical ultracentrifugaton, fluorescence anisotropy, NMR spectroscopy, and analytical chromatography, to understand the structural features of active compounds.